4.1 Spatial distribution characteristics of the epidemic
First, our findings show that in the initial stage the outbreak concentrations were typically located in the centrally built-up areas in a region’s economic, political, or transportation centers. These central built-up areas usually gather more city functions with well-developed built environments and excellent service, and thus cause a great population congregation, a high population density, and a high degree of human mobility, eventually becoming the harder-hit areas of the COVID-19 epidemic [26–28]. In other words, early in the outbreak, COVID-19 outcomes were typically highest in areas with high population densities, and this pattern was evident [29].
Second, the results indicated that within a city (macroscopically), as the level of the central built-up area of a region declines, the severity of the regional epidemic had been reduced. Besides, microscopically the farther a neighborhood is from the central built-up areas, the fewer cases it recorded [30]. These findings show that the spread of the pandemic in the early stages without intervention was not limited by administrative boundaries and distances, but by the structure and the social, economic, and cultural context of a city [18], which was reflected in the activities of the people involved.
To be more specific, structurally, towns in a city always tend to exhibit core-periphery characteristics [31–32], and the cores are often a city’s economic, political, or transportation centers macroscopically or the central built-up areas microscopically. The higher the level of administrative functions and the more prosperous the economy of a region, the stronger the attraction of the core, the closer the social and economic ties with other regions, the more active and concentrated the population, the more serious the epidemics were [28]. On the contrary, the epidemics were generally lower in periphery or suburban areas [33] because the density of the built environment is poor and the economy is not prosperous resulting in lower density, clustering, and mobility of people. The above analysis of the Wenzhou epidemic (3.2.2) also confirmed this point.
In terms of the social, economic, and cultural context, the mobility and connectivity also affect the spread of outbreaks, and their impacts may be greater than population density [34], which could be confirmed from the previous analysis (3.1.2) that Shenzhen's unique foreign population structure and Spring Festival population outflow hinder the local spread of the epidemic. Hence, epidemics can be controlled by regulating social and economic elements [35].
In summary, the spread of the epidemic presents a hierarchical decay and a core-periphery structure, and a decentralized built environment is less likely to create a large-scale epidemic cluster. The COVID-19 pandemic, which has dealt a heavy blow to the world's society and economy and has yet to subside, has led urbanists to rethink urban and architectural design [5, 36]. Is the current agglomerated urban form with high-rise buildings livable? How can cities coordinate the contradiction among the combined effect of economic development, epidemic prevention and control, and human well-being during the epidemic?
4.2 Future city planning and building design
During the lockdown period, the implementation of various social distancing measures by governments like closure of business service facilities and sports and recreational facilities, stay-at-home orders, and travel restrictions, caused the decrease of outdoor physical activity of urban residents [37], the shrinkage of social life in public places, and the decline of physical and mental health level in many populations and countries [38–39], and the increase of the frequency of tele-activities like teleconferencing, telework, telehealth, online learning, virtual meetings with friends and family, online live concerts, virtual weddings [40]. After the lockdown ends, people expressed an urgent need for social interaction in social spaces [41] and a strong desire to be close to nature in green spaces [42].
These phenomena caused by the COVID-19 epidemic indicate the necessity of transforming urban development patterns in the post-pandemic era. There might be some changes in the future urban social and living space. As the demand for green and outdoor activities surged during the pandemic period, small pocket parks and gardens had been created and parking lots been turned into parklets in cities like San Francisco, Birmingham [43]. And walking path and safe cycling along London's arteries and streets were created, and, more than 150 km of streets were announced to open for creating safe social recreation spaces in New York. Similar examples could be multiplied in Rome, Mexico, and other cities [44]. These temporary coping strategies revealed the disadvantages of current prevailing agglomerated urban form with high-rise buildings which is companied with high-density populations, high outbreak risk, limited green outdoor activity spaces and small indoor living space causing high pressure of epidemic control.
The city planning and building design should try to match the Sustainable Development Goals like sustainable cities and communities and good health and well-being and consider more about people's welfare like reducing the density of high-rise buildings, expanding outdoor activity spaces, and increasing green spaces than agglomeration economic effects. And many studies have already recommended that urban land use should be more evenly distributed and not concentrated in specific areas [45].
Both cities and villages have their own magnets, but obviously the superior social living conditions in cities have a stronger magnetic force, thus attracting 55% of the global population to live [8]. People want a better life, and they flock to cities because they think cities have better employment opportunities, higher wages, more social opportunities, and places of entertainment, etc.; city dwellers, however, yearn for the natural beauty, fresh air of the countryside [46]. Therefore, breaking the urban-rural dual structure, that is following the concept of Howard’s Garden City that combining the advantages of urban and rural areas to create a new settlement form [47], is the best solution to increase the resilience of communities, response to epidemics, and realize the good health and human well-being.
Besides, in the post-epidemic era, with the persistence of tele-activities, commuting may be no longer the main theme of urban residents, while spacious living space and green space may become the main needs of urban residents. And the offline physical spaces such as enterprise office space, sales space and traffic space might be reduced to some extent, while the minimum family living space would be increased to adapt to the production of home office, home garden [48], personal balcony and other living space. Such changes can save time spent commuting to work, reduce energy consumption, increase daily leisure time, and provide nature contact just in home, thus being functional and appealing even when there is no epidemic [49].
4.3 Urban medical carrying capacity
The carrying capacity of the six selected cities’ medical institutions was not overloaded during the epidemic, but that does not mean they could withstand a more severe outbreak. In fact, the COVID-19 pandemic posed great challenges to healthcare systems in many cities worldwide. During the severe outbreak in Wuhan, China, there were more than ten Fangcang shelter hospitals opened by converting exhibition centers and stadiums to address and cater for confirmed patients [50], and similar large ‘tent’ venues also had been erected in other countries. In Melbourne, Australia, a pre-fabricated semi-containerized two-story COVID-19 hospital in a car park was erected [51]. In London, United Kingdom, a 500 bed Nightingale Hospital with the capacity increased to treat approximately 4000 patients was created within the Excel Exhibition Center in the Docklands [52]. And India transformed spaces like train carriages to serve COVID-19 patients [53]. These instances all illustrate that medical facilities and their human resources are overwhelmed during the outbreaks [54]. Resources are limited, and the key is to think of ways to make full use of them.
Urban medical services during an epidemic are essentially the management, allocation, and efficient use of resources about people, places, and materials to confront the contradiction between supply and demand [55–56]. Above built fabric restructuring is an excellent example about the use of the static ‘place’ resource. As people and materials are movable, their management and distribution will be better with the support of big data, cloud computing, geographic information system (GIS), artificial intelligence (AI), and other technologies. Hence, there is need to construct a medical resource platform based on the dynamic database of medical personnel and supplies containing the professional background, skill level, career stage (in-service, internship, or school student), workplace, and home address of all (potential) doctors and nurses, as well as information on the name, production date, shelf life, storage location and quantity of medical products in storage and on the resource utilization and consumption in a region. Then, based on hospitals' real-time carrying capacity and resource consumption, the medical staff scheduling contingency plan and the backup medical supplies circulation replenishment plan can be automatically calculated and developed. Besides, maximizing the service life of medical equipment and the shelf life of medical products and developing a reusable, ultra-light, and intelligent mask is important for achieving materials’ large-scale long-term storage and avoiding waste of resources and environmental pollution [57].
Furthermore, with the development of the technologies above and the establishment of digital health systems [58], medical and therapeutic activities have become more flexible and location-independent. The telehealth service is a prime example that is expected to increase strongly and permanently [59–62]. Given this, it is essential to disseminate basic medical knowledge and develop nursing skills (which better be included in compulsory public courses in universities) to better accommodate the remote diagnosis and treatment and home care wards [63] to address the shortage of medical staff and hospitals during a pandemic [64].
4.4 Implications for prevention and control
An overview of the above, the spread of the COVID-19 epidemic at the early stage showed hierarchical and core-edge structural characteristics within cities, which is closely related to human activities. And the urban medical services during epidemics are essentially the contradiction between supply and demand among people, places, and materials. Therefore, the prevention and control of epidemics are ultimately the planning and management of human activities and limited resources, which must focus on human nature, respect for humanitarian principles, and be people-centered and inclusivity [65] and must be aided by information technologies (IT) like big data, the internet of things, and intelligent monitoring and control. "People" with different social, economic and cultural backgrounds and autonomous initiative are the most difficult to manage, and all activities are related to people, including the management and allocation of various limited resources. Thus, the construction of a regional integrated emergency management GIS [66] are crucial for the precise prevention and decision support [67], which forms a part of the smart city construction that has been confirmed to be conducive to pandemic control [13].
The regional integrated emergency management GIS should at least include a dynamic medical case geo-information database, a wisdom trip platform, and a medical resource platform (4.3).
Medical cases with spatial attributes especially the earliest confirmed cases could offer valuable information on high potential risk areas, hence they are extremely important for timely controlling the source of infection, interrupting transmission routes, and warning of new pandemics. So, it is necessary to construct a dynamic geo-information database of medical cases. And the database should be based not only on diagnosis and treatment data, but also on crowdsourced data. Because the crowdsourcing data, such as Chinese Ding Xiang Yuan, can provide geotagged high-frequency data and alternative information, improve the resolution of disease spatial-temporal analysis, and increase public health awareness through public engagement process [68–69].
And the wisdom trip platform should be constructed based on the dynamic geo-information database of medical cases above to ensure normal outdoor activities while reducing direct contact between people, as person-to-person contact are the major mode of SARS-CoV-2 transmission [70]. Before the nationwide lockdown in mid-March in Italy, spending time outdoors was allowed. Because of no deployment and no intervention, gardens and parks then became public gathering places, increasing the potential contagion risk and resulting in the close of gardens and parks and more strict outing restrictions [71]. Hence, the wisdom trip platform is indispensable. On the platform, all outdoor places available for people's activities in the high-risk areas should be mapped first (including unused driveways and parking lots in the control areas). Then, combined with the temporal geography method, the maximum number of safe trips in each region should be designed, and the number of trips be categorized and dynamically counted by each household, daily and hourly, to reasonably plan, arrange, and adjust the activity places and ranges, activity periods and frequencies of all people with outdoor activity needs. By this way, maximum efforts are made to meet the basic demands of people's outdoor activities in high-risk areas during the epidemic, and to regulate and promote their physical and mental health levels, to achieve efficient control of people's activities ultimately.
In addition, the epidemic spreads hierarchically and exhibits a core-fringe structure, and the built environment varies greatly among different social, economic, and cultural backgrounds. And different groups have different activity characteristics. Therefore, different detailed policies should be developed according to the specific conditions of the time and place. The concept like science first, hierarchical planning, situational awareness, people-oriented, individualized treatment, and eco-friendly should be used throughout the prevention and control process to maximumly meet people's needs, win their trust, and ultimately gain their support to fight the epidemic together.